When Indonesia’s Mount Tambora erupted in 1815, the world got an all too vivid glimpse at just how far-reaching the damage can be. The largest volcanic eruption in the earth’s history killed 100,000 people and caused ‘The Year Without a Summer‘, crop-killing summer snow and freezing temperatures in the United States and Europe. Today, Iceland’s Mount Eyjafjallajökull is far from the only one to worry about.There’s an unusual amount of seismic activity happening everywhere from Washington State to North Korea, with 12 deadly volcanoes nearing potential eruption.

Katla Volcano, Iceland

If you thought Iceland’s Eyjafjallajökull eruption was bad, you haven’t seen anything yet. Think of the Katla volcano as Eyjafjallajökull’s fiercer, angrier, more violent sister. A Katla volcano eruption would be ten times stronger and would shoot larger plumes of ash much higher in the air. Though experts feared that Katla might be set off by the eruption back in April, it hasn’t happened yet – but that doesn’t mean it won’t.

Mount Baekdu, North Korea

Mount Baekdu is sacred to Koreans, deeply connected to their history – the legend goes that this volcanic mountain on the border between North Korea and China is the ancestral origin of their people. But it may soon be connected to a new, less positive legend; experts believe it’s going to erupt for the first time since 947 A.D. sometime between 2014 and 2015. Last time, the amount of ash created is estimated to have been 1,000 times that of the recent Iceland eruption.

Mayon Volcano, Philippines

In December of 2009, residents of the central province in the Philippines got the warning: evacuate, because Mayon is going to blow any time now. Tens of thousands of people fled the area as Mount Mayon began to hiss steam and spew ash into the air and lava began to pour down the mountainside. Ultimately, the volcano didn’t erupt – not yet, at least. The warning level has been lowered since then, but experts say the danger is far from past, especially as volcanic earthquakes and rockfall events continue to occur.

Mount St. Helens, Washington, USA

30 years ago, Mount St. Helens caused utter chaos in Washington State, killing dozens of people and decimating more than 200 square miles of forest. It erupted again in 2004 – much more mildly – but another eruption is just a matter of time, and there would be very little warning once it began. Scientists estimate that Mount St. Helens would send a plume of ash 30,000 feet into the sky within five minutes.

Yellowstone Volcano, Wyoming, USA

When Iceland’s volcano erupted in April 2010, the most damage it did was to the airline industry as billions of dollars were lost to grounded flights. But, as CBS News puts it, “If the Yellowstone volcano has a major eruption, you won’t be thinking much about flying.” That’s because this gigantic little-known volcano, which lies under the surface of one of America’s most popular national parks, would level nearby towns and cover a huge portion of the central US with dozens of feet of ash if it erupted. Right now, the rock is about 5% molten, and it needs to reach 15% before an eruption – which could happen in a matter of days, but would have to be triggered by a major event about as likely as a mile-wide asteroid hitting the earth. The Yellowstone volcano is being carefully monitored by scientists, so we’ll likely know far ahead of time if this baby gets ready to blow.

Marsili Volcano, Italy

As if Southern Italy didn’t have enough volcanic threats, there’s also the possibility of a nearby undersea volcano collapsing and causing a catastrophic tsunami. In that sense, the Marsili Volcano isn’t technically “about to blow” – but it could cause just as much damage. In fact, experts at the National Institute of Geophysics and Volcanology say that the volcano’s walls could crumble at any time, producing shock waves that could theoretically sink the whole of Southern Italy into the Mediterranean Sea. It’s not a matter of if, but when – however, that ‘when’ may not occur for hundreds of years.

Glacier Peak, Washington, USA

Compared to the majesty of nearby Mount Rainier and Mount Baker, Washington State’s Glacier Peak seems like a mole hill. But buy a home in Snohomish County, and you’ll be forced to sign a document acknowledging your awareness of the fact that you’ll be living within the volcano’s reach. Glacier Peak is one of 18 U.S. Volcanoes listed as “very high threat”, but it has only three siesmometers and no GPS monitoring stations. Its last major eruption was about 1800 years ago, and when it erupts again, it will be far more violent than the 1980 eruption of Mount St. Helens.

Mount Vesuvius, Italy

The 1 million people who live at the base of Mt. Vesuvius don’t need to be reminded of the horrors that another eruption of that infamous volcano would bring – they know all too well. Pompeii, completely annihilated in the year 79 B.C.E., is just minutes from the bustling metropolis of Naples, Italy. Yet another eruption killed 4,000 people in 1631, while a 1944 eruption took the lives of 26. Vesuvius is now considered Italy’s “biggest public safety problem”, though no one can predict when it will next awaken. Luckily, the chance of another Pompeii-sized eruption is only around 1 percent.

Ischia Volcano, Italy

Not far from Mount Vesuvius, just a few miles away off the coast of Southern Italy, lies yet another volcano that could potentially erupt at any time – and while it’s far less known than Vesuvius, it may be even more dangerous. Ischia last erupted 700 years ago, and scientists say that it’s experiencing a build-up of magma that may be a disturbing hint at coming events.

Mount Merapi, Indonesia

It’s a beautiful sight, towering over the surrounding flat lands with their jumbles of bright-roofed buildings. But Mount Merapi is also deadly, and capable of meting out an incredible amount of destruction. It has earned its place among the world’s most active volcanoes, with mild eruptions occurring every 2-3 years, larger ones every 10-15 years and exceptionally lethal eruptions happening every 40-60 years. In 1930, 1400 people lost their lives and 13 villages were destroyed; in 2006, the volcano threatened to blow but seismic activity calmed down within a couple weeks.

Nyiragongo, Democratic Republic of Congo

Just like its similarly volatile neighbor Nyamuragira, the volcano Nyiragongo – located in the Democratic Republic of Congo – is extremely active, having erupted at least 34 times since 1882. A major eruption in 2002 sent lava pouring into the streets of nearby towns. Another one is likely forthcoming: in June 2010, a massive plume of molten rock associated with volcanic activity was discovered heading toward the East African Rift upon which Nyiragongo sits.

Taal Volcano, Philippines

In the Philippines, residents are on alert for a possible eruption of the Taal Volcano, which could blow for the first time since 1997. Located just 30 miles south of the densely populated capital city of Manila, Taal could cause significant upheaval in the region including fatalities. The volcano began hissing steam last year and many high-frequency volcanic earthquakes were detected in the third week of June 2010, with magma currently moving toward the surface.